The broad long-term goal of the proposed work is to understand the molecular basis for tumor progression in prostate cancer. To that end we propose in the year of R21 funding to develop methods that can image gene expression patterns in living cells. We focus our study on the alternative splicing of fibroblast growth factor receptor type 2 (FGF-R2) transcripts. This alternative splicing results in the production of two FGF-R2 isoforms, FGF-R2(IIIb) and FGF-R2(lllc), which have very different ligand binding properties. The choice of FGF-R2(lllb) vs. FGF-R2(lllc) is highly regulated during development and is deregulated during prostate tumor progression. R21 Specific Aim No. 1: Construction and testing of real time reporters of alternative splicing of FGF-R2. We will design and construct reporter plasmids capable of imaging changes in gene expression due to alternative splicing. Alternative splicing regulation will be imaged by measuring fluorescence, luminescence and expression of MRI detectable proteins. Studies will be carried out in tissue culture to prove the utility of these plasmid reporters. In the three years of R33 support we propose to develop methods that can image gene expression patterns in tumors and in living animals. We focus our study on the alternative splicing of fibroblast growth factor receptor type 2 (FGF-R2) transcripts in prostate tumors in rats and in nude mice. We also propose to study the regulation of this alternative splicing in normal tissues in transgenic mice. In order to achieve these goals we propose to accomplish the following two specific aims: R33 Specific Aim No. 1: To evaluate the alternative splicing of FGF-R2 in prostate tumors in living animals. We propose to use the imaging reporters designed and built during the R21 year to study the transition from FGF-R2(lllb) to FGF-R2(lllc) that accompanies the progression of prostate tumors. We will evaluate two prostate tumor model systems, the Dunning rat prostate model in syngeneic immunocompetent rats and the LnCAP human xenograft in nu/nu mice. R33 Specific Aim No. 2: To evaluate the alternative splicing of FGF-R2 in normal tissues of transgenic mice. We will employ the aforementioned imaging reporters to study the regulation of alternative splicing in living animals. We hope to provide an anatomic map of gene expression based on alternative splicing regulation.